This invention relates to the securing of anchor bolts in drilled openings in a mine roof for supporting the roof.
Mine roof bolts of the expansion shell type have been widely used for supporting mine roofs. In more recent years, resin anchors have been employed. In the resin type anchor, a resin and catalyst cartridge is inserted into the back of a mine roof opening, following which an anchor bolt is forced upwardly into the opening, thereby rupturing the cartridge to permit the resin and catalyst to gravitate downwardly between the bolt and the wall of the opening. Upon mixing of the catalyst and resin, the resin sets to secure the bolt in the mine roof. In the use of resin type anchors, difficulty has been experienced in properly mixing the resin and catalyst to produce the greatest securing effect, and preventing either undermixing or overmixing of the resin and catalyst.
Resin has also been employed to reinforce or bond expansion shells in mine roofs as illustrated in U.S. Pat. Nos. 3,702,060 issued Nov. 7, 1972, 4,160,614 issued July 10, 1979 and 4,162,133 issued July 24, 1979. U.S. Pat. Nos. 4,160,614 and 4,162,133 mix the resin and catalyst by rotating the bolt in one direction, and actuate the expansion shell by rotation of the bolt in the opposite direction. Additionally, U.S. Pat. No. 3,188,815 issued June 15, 1965 discloses an anchor bolt assembly wherein a resin and catalyst cartridge is punctured by the tip of the roof bolt, following which the bolt is rotated a predetermined number of times for the purpose of mixing the resin and catalyst, an expansion shell carried by an intermediate portion of the bolt then being urged to its expanded position to grip the mine roof.
It has been found, however, that with all of the above combination anchors, there is great difficulty in securing a proper mixture of the resin and catalyst, with a consequent reduction in the effectiveness of the resin in securing the assembly in the mine roof opening. Also, where a sequence of separate and distinct operations are required to mix the resin and catalyst and then to activate the expansion shell, installation time is necessarily increased along with the danger of improper installation.